Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Imaging System, Method, and Applications
Field of the Invention
Aspects and embodiments of the invention are most generally directed to an
optical
imaging system, methods pertaining thereto, and applications thereof; more
particularly to a
panoramic optical imaging system, methods pertaining thereto, and applications
thereof; and,
most particularly to a panoramic optical imaging system that has zero or
substantially no
parallax, methods pertaining thereto, and applications thereof.
Brief Description of the Figures
Fig. 1 illustrates the chief ray of an optical system. The chief ray defines
the height of
the object as well as the height of the image.
Fig. 2 illustrates why parallax occurs when multiple refractive imaging
systems are
used to capture an image of a scene. In the lens unit on top, the three
objects are mapped to
the same image point; in the bottom lens unit they are mapped to three
separate image points.
Fig. 3 (left) illustrates the image formed by the top lens unit in Fig. 2,
whereas the
image on the right is that formed by the bottom lens unit.
Fig. 4 shows the image that would result from combining the two images in Fig.
3.
Fig. 5 illustrates how parallax occurs in the cameras created today. The field
of views
overlaps and a triangle that appears at the edge of the FOV for the bottom
lens system will
appear at around 0.707 times the FOV in the imaging system on top. Thus, the
triangle is
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mapped to different image points for each camera. On bottom it is mapped to
the full FOV
(the edge of the image).
Fig. 6 illustrates two imaging systems side by side which do not have
parallax. The
chief rays at the edge of each system are constrained to lie parallel one
another. Thus, objects
lying along this line are imaged to the same point in the image plane.
Fig. 7 illustrates the location of the non-parallax (NP) Point (as defined
below) for
both imaging systems shown.
Fig. 8 shows that the chief rays at the edge of the FOV are not parallel, thus
the NP
Points lie in different locations.
Fig. 9 illustrates an imaging system with NP Point lying before image sensor.
Fig. 10 illustrates two imaging systems aligned such that the chief rays at
the edge of
each ones FOV is parallel to the other.
Fig. 11 shows an imaging system with NP Point behind the image plane.
Fig. 12 shows a multiple unit imaging system with NP Points co-located.
Fig. 13 shows a 3-dimensional representation of a 360 degree lens system with
edge
rays constrained to lie along each dodecahedron face.
Fig. 14 shows a circle inscribed in a pentagon illustrating blind spots that
would be
created if lens was a circle rather than a pentagon.
Fig. 15 shows the first lens element of each system, initially designed to
circumscribe
regular pentagons.
Fig. 16: The diameter of the first lens element is constrained to be 1.7013a,
where a is
the side length of the regular pentagon.
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Fig. 17: The distance from the center of the first lens element to the center
of the
dodecahedron (NP Point) is 1.1135a where a is the side length of the pentagon.
Fig. 18: The distance from the top of the pentagon face to the NP Point is
constrained
to be 1.31a where a is the side length of the regular pentagon. Here the NP
Point is the center
of the dodecahedron.
Fig. 19: Diagram illustrating the constraints imposed on the first lens
element with
respect to the center of the dodecadron. "a" is the side length of each
regular pentagon in the
dodecahedron.
Fig. 20: Diagram illustrating that the maximal length of any element is
constrained to
fit within the 31.717 degree half angle cone of light emanating from the
center of the
dodecahedron.
Fig. 21: Three-dimensional representation of 1/12th of dodecahedron and angle
between center of dodecahedron and center of pentagon edge.
Fig. 22: Three-dimensional representation of 1/12th of dodecahedron and angle
between center of dodecahedron and edge of pentagon edge.
Fig. 23: Pentagon shaped lens element showing height to ray 1 and ray 37.
Fig. 24: Zemax diagram of current lens design showing Rays 1 and 37 in model.
Fig. 25: Three-dimensional Zemax diagram of current lens design from back.
Fig. 26: Three-dimensional Zemax diagram from side.
Background
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Description of Related Art
Current 360 degree systems without parallax employ an arrangement of mirrors
to
scan the image and are limited by an imaging speed of 10 frames per second
(fps). Google
uses a 360 degree camera with refractive lenses developed by Immersive Media
to capture
photos for its Streetview software. The photos must be post-processed and
corrected for
parallax, costing time, which reduces Google's ability to scale its Streetview
initiatives.
Fisheye lenses provide wide angle imaging but at the cost of high distortion.
Distortion is the
physical result of mapping a large spherical object onto a small flat image
plane.
Some companies have developed optical systems to simplify the process of
taking a
panoramic image. Rather than rotating the camera to get multiple shots, all of
the photos are
captured simultaneously with many cameras imaging different parts of the
scene. Immersive
Media and Greypoint Imaging have developed single shot 360 degree cameras that
are
available for varying price tags between $10,000 and $100,000. Both companies
develop
software to automatically correct for the artifacts (parallax) created in the
image and offer a
better solution than panoramas captured by one camera, e.g., the iPhone
camera. The
software, however, is not perfect and many artifacts still exist in the
images. Anecdotally,
Google, had one person carry a Dodeca 360 camera (offered by Immersive Media)
around the
Grand Canyon, and had to employ programmers to correct the images frame by
frame for the
artifacts induced by parallax.
Parallax and the Chief Rays of an optical system
Parallax is defined as "the effect whereby the position or direction of an
object
appears to differ when viewed from different positions, e.g., through the
viewfinder and the
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lens of a camera." Parallax is created as a result of stitching together
images from multiple
cameras, each with its own unique perspective of the world.
Referring to Fig. 1, the chief ray of an optical system is the meridional ray
that starts
at the edge of an object, crosses the center of the optical axis at the
aperture stop, and ends at
the edge of the image at the detector. Thus the chief ray defines the size of
an image.
The chief ray plays a critical role in the parallax created by stitching
together multiple
images. Fig. 2 illustrates two optical systems (cameras) side by side. For the
lens unit on top,
the square, triangle and rectangle are mapped to the same point in the image,
whereas for the
lens unit on bottom they are mapped to three distinct points as shown. In the
top imaging
system, they are imaged by the same chief ray, whereas for the bottom imaging
system, they
are imaged by three distinct chief rays. When combining the two images in Fig.
3, parallax
would occur and an image as shown in Fig. 4 would result.
The search for an algorithm that can correct for parallax has been going on
for many
years. Many solutions have been developed but even with the most sophisticated
algorithms
to date, artifacts are still left in panoramic images. For some, this may not
be a problem as
software engineers can be hired to fix the images frame by frame; however, for
the general
consumer this option of correcting each image is not feasible. A better
solution is needed that
effectively corrects for parallax before such a system can be made available
to the consumer
market. It is preferable to solve the problem of reducing parallax in an image
optically, rather
than computationally.
Current designs created for single shot panoramic imaging suffer from parallax
because they are created from imaging systems with overlapping fields of view.
Fig. 5 is
taken from U.S. Patent 2,696,758. This figure illustrates how parallax is
created in the 360
degree imaging systems available today. The field of views overlap and a
triangle that
Date Recue/Date Received 2022-03-07
appears at the edge of the FOV for the bottom lens system will appear at
around 0.707 times
the FOV in the imaging system on top. Thus, the triangle is mapped to
different image points
for each camera. On the bottom it is mapped to the full FOV (the edge of the
image).
The inventor has thus recognized the advantages and benefits of a panoramic
imaging
system and associated methods in which there is no parallax, and where the
parallax is
eliminated optically rather than by post-processing software. Such a system
would have
applications including providing a scalable way to map the streets of the
planet; allowing for
the creation of virtual tours, both of cities and of private institutions;
high frame-rate video
surveillance; military applications including drone and tank technology; an
alternative for
fisheye lenses which provide wide angle imaging at the cost of high
distortion.
Summary
An aspect of the invention is a multicamera panoramic imaging system having no
parallax. According to a non-limiting embodiment, the multicamera panoramic
imaging
system includes a plurality of discrete, imaging systems disposed in a side-by-
side array,
wherein a field of view of each discrete, imaging system is conjoined with a
field of view of
each adjacent discrete imaging system, further wherein a stencil of chief rays
at the edge of
the field of view of any one of the discrete imaging systems will be
substantially parallel to a
stencil of chief rays at the edge of the field of view of any adjacent ones of
the discrete
imaging systems such that all of the substantially parallel stencils of chief
rays appear to
converge to a common point when viewed from object space. In various non-
limiting
embodiments, the multicamera panoramic imaging system may include or be
further
characterized by the following features, limitations, characteristics either
alone or in various
combinations thereof:
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-comprising a plurality of identical discrete imaging systems;
-wherein at least 50% of the stencil of chief rays deviate from parallel by
twenty degrees or less;
-wherein each of the discrete imaging systems includes an image sensor,
further wherein the
apparent convergence point lies behind the image sensor of each of the
discrete imaging systems;
-wherein none of the discrete imaging systems physically overlap;
-wherein the system has a dodecahedron geometry, further wherein the system is
characterized
by a 360 degree FOV;
-wherein a front lens of each of the discrete imaging systems is a portion of
a single, contiguous
freeform optic;
-wherein each image sensor is a wavefront sensor;
-wherein each of the discrete imaging systems has a curved image plane so as
to match a
distortion and Petzval Curvature of the imaging system.
An aspect of the invention is a method for forming an image of an object
having no
parallax. According to a non-limiting embodiment, the method includes
providing a panoramic
imaging system, wherein the panoramic imaging system comprises a plurality of
discrete
imaging systems each characterized by a field of view; and constraining a
stencil of chief rays at
the edge of the field of view of every one of the discrete imaging systems to
be substantially
parallel to a stencil of chief rays at the edge of the field of view of an
immediately adjacent one
of the discrete imaging systems such that all of the parallel stencils of
chief rays appear to
converge to a common point when viewed from object space, wherein the imaging
system is
parallax-free. In various non-limiting embodiments, the panoramic imaging
method may include
or be further characterized by the following features, limitations,
characteristics, steps either
alone or in various combinations thereof:
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-further comprising constraining at least 50% of the stencil of chief rays to
deviate from parallel
by twenty degrees or less;
-further comprising using an algorithm to correct a distortion aberration in a
contiguous 360
degree image formed by the imaging system.
An aspect of the invention is a method for designing a (substantially)
parallax-
free, panoramic imaging system. According to a non-limiting embodiment, the
method includes
determining an overall panoramic imaging system geometry, wherein the overall
panoramic
imaging system comprises a plurality of discrete, imaging systems having
respective fields of
view, disposed in a side-by-side array such that the fields of view of
adjacent imaging systems
conjoin; designing the discrete imaging systems such that a stencil of chief
rays at the edge of the
field of view of one of the discrete imaging systems will be substantially
parallel to a stencil of
chief rays at the edge of the field of view of an adjacent one of the discrete
imaging systems such
that the substantially parallel stencil of chief rays would appear to converge
to a common point
when viewed from object space. In various non-limiting embodiments, the
panoramic imaging
method may include or be further characterized by the following features,
limitations,
characteristics, steps either alone or in various combinations thereof:
-wherein the overall panoramic imaging system comprises a plurality of
identical discrete
imaging systems;
-wherein in designing the discrete imaging systems, ensuring that there is no
physical overlap
between any of the plurality of the discrete imaging systems;
-wherein in designing the discrete imaging systems, ensuring that the apparent
convergence point
lies behind a respective image sensor of each discrete imaging system.
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Detailed Description of Exemplary, Non-limiting Embodiments
For a panoramic camera to achieve minimal parallax, the field of views (FOV)
of the
imaging systems must not overlap. Thus, the chief ray at the edge of the FOV
must approach the
optical system parallel to the chief rays at the edge of the adjacent optical
system.
Fig. 6 illustrates two imaging systems side by side which do not have
parallax. The chief
rays at the edge of each system are constrained to lie parallel one another.
Thus, objects lying
along this line are imaged to the same point in the image plane. This is an
approach that can be
used to design the individual lens elements. The fields of view do not overlap
one another
because the chief rays at the blending angles are constrained to be parallel
to one another and
converge to a common point. The common point will depend on the geometry in
which the
lenses are encased. In other words, the chief rays are constrained to be
parallel such that they
appear to cross the optical axis at the same point when viewing the lens
system from object
space. In actuality, they cross the optical axis at an image sensor, which
lies before this
imaginary point, but it appears, looking into the lens system from object
space, that they cross at
the same point.
NP Point (No Parallax Point)
To aid in the understanding of the previous concept, we define a term referred
to as the No
Parallax Point (NP Point). The NF Point is an abstraction used for
understanding how the chief
rays at the edge of the FOV can physically be made to lie parallel to one
another and what rules
they should follow. The NP Point is the point where the chief rays at the edge
of adjacent optical
systems intersect the optical axis when viewing the system from object space
for a panoramic
imaging system without parallax.
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According to the embodied invention, the NP Points for each imaging system
must lie in
the same location. That is to say, that the rays of adjacent optical systems
must be parallel. Fig. 9
shows an imaging system with the NP Point lying in front of the imaging
sensor. Fig. 10
illustrates two imaging systems aligned such that the chief rays at the edge
of each one's FOV is
parallel to the other. This constraint means that the NP Point must be at the
same location for
both systems. When the NP Point is in front of the image sensor, it is
impossible to align the NP
Points without the lens elements overlapping. This system would not have any
parallax, but it is
physically impossible to implement. This indicates that when designing the
optical system, the
NP Point should lie behind all of the elements in the imaging system so that
no elements
physically overlap with one another.
Fig. 11 shows a system where the NP Point lies behind the image plane. When
this is the
case, it is possible to arrange multiple imaging systems such that the fields
of view do not
overlap, as shown in Fig. 12. The exact location of the NP Point will be
determined by the
geometry of the lens arrangements. By arbitrarily picking a location, that is
to say arbitrarily
choosing a ray height and incident angle such that the chief ray appears to
cross the optical axis
behind the image plane, the geometry of lens systems may require hundreds of
lens units to
capture a full 360 degree image. The NP Point location must be determined
after considering the
geometry one may wish to use for the lenses.
An embodiment of the present invention relates to a multicamera panoramic
imaging
system, where the fields of adjacent imaging units merge to form the composite
field of view of
the entire imaging system, as illustrated in the schematic of Fig. 7.
Traditional panoramic
imaging systems put together imaging units in such a way that their respective
fields of view
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overlap as illustrated in the schematic of Fig. 8, which leads to parallax in
the resulting images,
and requires corrective software to stitch the images together to remove the
parallax.
In the instant exemplary embodiment, the rays striking the edge of one imaging
unit are
constrained to lie parallel to the incoming rays of an adjacent imaging unit
so that both imaging
systems share the same set of edge rays. As seen in the 3-dimensional model of
Fig. 13, the rays
at the edge of one imaging unit are the same as those at the edge of an
adjacent imaging unit. The
rays are the gray lines constrained to lie along the surface of the
dodecahedron edge. The gray
rays at the edge of each pentagon shaped lens are coincident to the rays
entering its neighboring
surface. All rays at radii beneath the edge rays lie at smaller angles of
incidence so that these
rays do not overlap rays from adjacent systems.
The embodied panoramic imaging system utilizes the aforementioned technique of
designing an imaging system with a NP point behind the image sensor, and
combines multiple
lens systems in a dodecahedron geometry, to create a 360 degree FOV camera
with minimal or
no parallax.
The first lens element will be shaped into the surface of a regular pentagon.
The
complete system will be composed of 12 discrete imaging units, each with a
common NP point
for rays along the edge of the pentagon and constrained to have incident
angles meeting the
geometry specified by that of a dodecahedron.
A dodecahedron is a polyhedron with 12 surfaces. A polyhedron is a three
dimensional
solid consisting of a collection of polygons joined at the edges. Each side of
the dodecahedron is
a regular pentagon (a pentagon with equal length sides). Dodecahedrons have
some important
geometrical properties that must be understood in order to design a lens
system utilizing the
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geometry. The properties will be discussed in turn next after briefly
discussing why the first lens
must be shaped into the surface of a pentagon.
By using a circularly edged lens as the first element in the dodecahedron
geometry, it is
not possible to capture all information in the 360 degree field of view using
the current technique
of aligning edge rays. The missing area from where the first lens is inscribed
in the pentagon
(shaded region in Fig. 14) creates blind spots. Because the fields of view
never overlap, this
information is never captured. It can be calculated that the ratio between the
area of a circle to
the area of a pentagon it is inscribed in is equal to 7r/5 or 62.83%. This is
the maximal amount of
information that we can record for the 360 degree field around us. Blind spots
created between
the lens and the pentagon delete nearly 40% of information in the 360 degree
image.
The following description is meant to illustrate the geometry of a
dodecahedron and is
necessary when creating a lens system utilizing the aforementioned NP
technique and a
dodecahedron geometry, but is not essential for the purposes of creating the
no parallax,
panoramic imaging system embodied herein.
Property 1: Diameter of circle circumscribing regular pentagon
For each of the 12 individual lens systems, the first lens will be designed
such that it
circumscribes each of the regular pentagons of the dodecahedron as shown in
Fig. 15. The
diameter of a circle circumscribing a regular pentagon is:
D = a/sin (36 ) = 1.7013a
In the equation above, "a" is the side length of the regular pentagon. The
first lens
element of each system will fully circumscribe each pentagon and so the
diameter of the first
lens element for each system is given as 1.7013a as illustrated in Fig. 16.
Property 2: Inscribed sphere touching center of each pentagon
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The radius of an inscribed sphere (tangent to each of the dodecahedron's
faces) is:
15 si7 . . =
5) P:s 1. 11.35) 1 bo64
2 V 1 0
This radius is the distance from the center of the dodecahedron, which will be
the NP Point for
each lens in this design, and the center of the pentagon's face, which
coincides with the center
(optical axis) of the first lens element in a system occupying that pentagon.
This point is at the
center of each pentagon face. The length between the NP point and the center
of the
dodecahedron is constrained to be 1.1135a where a is the length of one of the
pentagon sides, as
illustrated in Fig. 17.
Property 3: Mid-radius of Dodecahedron
The mid-radius is the point connecting the center of the dodecahedron and the
middle of
each edge. This length is given as follows:
1. I
r = :a-, 13 4- V5 Lot. '190 b994 a - =
mt.
This equation constrains the distance between the top of the pentagon face and
the NP Point, as
illustrated in Fig. 18.
Constraints
The geometric properties of a dodecahedron constrain the design of the 12
lenses that will
embody it. In particular, we have the following four parameters based upon the
description
given above:
1. Diameter of 1st lens element: 1.7013a;
2. Distance from 1st lens element to center of dodecahedron: 1.1135a;
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3. Distance from top of 1st lens element to center of dodecahedron: 1.31a;
4. FOV = 37.3777 degrees
Given any two of the first three constraints, we have that the angle between
the optical axis of
the lens and the top of the first lens element is 37.3777 degrees (see Fig.
19):
tan ((1.7013/2)/1.1135) ¨ 37.3770
.
We want this angle of 37.37 degrees to be the field of view of the lens. This
will ensure that the
NP Point, that is the point where the chief ray of the blending (the blending
angle being the full
FOV) intersects the optical axis in object space, lies at the center of the
dodecahedron. All of the
other constraints will ensure that the lens elements lie before the NP Point
and that the elements
fall within the 31.717 degree half angle cone of light.
Diameter of Other Lens Elements and Sensor
With the four constraints given above, we know what the size of each lens
element after
the first must be in order to fit into the dodecahedron geometry. In order for
the preceding lens
elements to fit, any lens or sensor element must fit inside of the 31.717
degree cone of light
beginning at the center of the dodecahedron and tangential to the diameter of
the first lens
element. As the distance from the first lens element increases, the diameter
of the preceding lens
elements will decrease proportionally (see Fig. 20).
The maximum diameter of any lens element or sensor preceding the first can be
found
geometrically to be less than or equal to (1.1135a ¨ D)*tan (31.716 degrees)
where D is the
distance of that element from the first lens element.
Thus, we now have the five constraints that will allow this lens system to
match the
geometry of a dodecahedron and permit 360 degree imaging:
1. Diameter of 1st lens element: 1.3763a;
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2. Distance from 1st lens element to center of dodecahedron: 1.1135a;
3. Distance from top of 1st lens element to center of dodecahedron: 1.31a;
4. FOV = 37.377 degrees;
5. < (1.1135a - DLL Li) tan (31.717 ),
where cOLi is the diameter of any lens element separated by a distance Dil, Li
from the first. Given
the above five constraints, where all lenses are designed such that they fall
within the 31.717
degree cone of light emanating from the center of the dodecahedron, it is
possible to construct a
lens system without parallax.
System Design
A geometry for the lenses was chosen. Platonic solids have the property that
they are
composed of many solids of equal geometry and volume. For a system imaging 360
degrees,
this allows the composite imaging system to be made from the same replicated
lens design. A
dodecahedron geometry was chosen because it is approximately spherical in its
geometry.
In order for the edge rays of one imaging unit to lie parallel to those of an
adjacent unit,
they must enter at the same angle. The angle shared by both imaging units is
that of the
dodecahedrons edge surface. At the center of the edge surface, the angle with
respect to the
center of the dodecahedron center is 31.717 degrees, as illustrated in Fig.
21. At the corner of
the edge surface, the angle with respect to the center of the dodecahedron
center is 37.377
degrees, as illustrated in Fig. 22.
In order to make the rays along adjacent imaging units match, the first lens
of the
imaging unit is cut into a pentagon, matching the surface of the dodecahedron.
At the center of
the edge, the ray striking the surface enters with an angle of incidence of
31.717 degrees. At the
corner of the edge, the angle of incidence of an entering ray is 37.377
degrees. At all points
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along the edge of the lens, the angle of incidence of an entering ray is made
to match the
geometry of the dodecahedron surface.
The angle of incidence for 37 rays along the edge of the pentagon lens was
calculated
using trigonometry, knowing the distance from the center of the dodecahedron
to the center of
the pentagon face, and knowing the distance from the center of the
dodecahedron to the edge
point in question as shown in the figures 21 and 22. The height of each ray
was constrained to
lie along the pentagon edge. For example, with a radius of 120 mm describing
the circumscribed
circle of surface 1, the ray at point 1 has a height of 48.54 mm and an angle
of incidence of
31.717 degrees. The ray at point 37 has a height of 60 mm and an angle of
incidence of 37.377
degrees. Table I describes the values for ray heights and angle of incidence
for 37 points
between Point 1 and Point 36 in Fig. 23.
Table I
(Data showing constraints on 37 rays lying along the edge of the first lens)
Point Ray Height Angle of Incidence
1 -48.54101966 31.71747441
2 -48.55131914 31.72137741
3 -48.58220446 31.7330904
4 -48.6336364 31.75262531
5 -48.70554989 31.78000204
6 -48.79785436 31.81524851
7 -48.91043437 31.8584007
8 -49.04315028 31.90950275
9 -49.19583915 31.96860698
10 -49.36831565 32.03577404
11 -49.56037318 32.111073
12 -49.77178508 32.19458149
13 -50.00230585 32.28638584
14 -50.25167251 32.38658121
15 -50.51960599 32.49527181
16 -50.80581256 32.61257109
17 -51.10998523 32.7386019
18 -51.43180524 32.87349676
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19 -51.77094349 33.01739809
20 -52.12706197 33.17045845
21 -52.49981514 33.33284086
22 -52.88885128 33.50471903
23 -53.2938138 33.68627773
24 -53.7143425 33.87771306
25 -54.1500747 34.07923284
26 -54.60064642 34.29105695
27 -55.0656934 34.51341771
28 -55.54485206 34.74656026
29 -56.03776039 34.99074298
30 -56.54405884 35.2462379
31 -57.06339098 35.51333115
32 -57.59540424 35.7923234
33 -58.13975051 36.0835303
34 -58.69608667 36.38728295
35 -59.26407504 36.70392839
36 -59.84338384 37.03383003
37 -60 37.37736813
A diagram illustrating the ray constraints is shown in Fig. 24. Ray 1 has a
height of
48.54 mm and an angle of incidence of 31.717 degrees. Ray 1 is the ray going
through point 1 in
Fig. 24. Ray 2 has a height of 60 mm and an angle of incidence of 37.377
degrees and is the ray
going through point 37 in Fig. 24. All 37 rays are constrained by the ray
heights and angles
specified in the table above. Constrained in this way, all rays enter the lens
at the same angle as
the surface of the dodecahedron. Looking at those same rays in another way, we
can see that the
rays are constrained properly to a pentagon geometry at the correct angles of
incidence, as
illustrated in Figs. 25 and 26.
17
